1. Field of Invention
The present invention relates to a method for synchronization for use in data transmission and more particularly to a method for word synchronization that can be used in systems with multiple serial links.
2. Description of Related Art
The problem of word synchronization results in communications systems with multiple serial links where each link carries a portion of a word being transmitted. For example, a 64-bit word may be transmitted between two word devices as eight 8-bit bytes, the arrival of which must be synchronized so that the 64-bit word arrives correctly. In order to enable this synchronization in a robust way, requirements for handshaking go beyond what has been developed for a single serial link. For example, the Next Generation I/O Link Architecture Specification describes link establishment and maintenance handshaking together with an associated state machine but only for a single serial link. There is no generalization to the concept of word synchronization on multiple serial links. (NGIO Specification, Oct. 30, 1998, Intel Corporation; http://developer.intel.com/design/servers/future_server_io/ for an overview, and http://devloper.intel.com/design/servers/future_server_io/documents/ngiolas.pdf for the complete document.)
Likewise, Fibre Channel specifications provide link states and link establishment handshaking but only for a single serial link. (ANSI X3.230:1994, Fibre Channel Physical and Signaling Interface (FC-PH) Rev 4.3)
Only limited word synchronization has been developed for multiple serial devices. The Vitesse quad SERDES (serializer/deserializer) device provides the capability to synchronize multiple serial links but without any status, confirmation or link state handshake, features that are essential to a robust implementation. (Vitesse Quad SERDES VSC7216 specification; Vitesse Quad SERDES VSC7214 Specification: http://www.vitesse.com/summarysheets/vsc7214.htm.) For example, in the absence of handshaking, data may be sent without synchronization and errors may develop and go undetected.
There are many ways of encoding data to send it over a serial data link. The most widely used is an 8-bit to 10-bit encoding defined in the Fibre Channel PH Specification cited above. This encoding allows the receiver to recover a clock for sampling the data and to detect byte boundaries in the data. It also provides for the transmission of non-data control characters. While Fibre Channel defines a use for some control characters, they call be assigned other uses when the encoding is used separately from Fibre Channel. There are other less widely used encodings with similar features. These encodings, including that used by Fibre Channel and others, will be referred to hereinafter as FC-like serial encoding. A serializer or deserializer that uses an FC-like serial encoding will hereinafter be called a SERDES.